High vacuum diffusion pump



Feb. 2, 1954 J. WISHART HIGH VACUUM DIFFUSION PUMP Filed March 5, 1952 ATTORNEYS T. A Hm L b V wmw, 2 s E G u w A E J M 5 3 2. 2 M. B l 0x 7 l 3ag m m H w. a 4m 3% MM C 3 3 3 I7 0 P W31 Al .m l m 5 .1. M w n i 0/ 8 Kd 6 6 4 '8 4 3 3 0 5 5 l/ all I 0 2 M a H Patented Feb. 2 1954 HIGHVACUUM DIFFUSION PUMP James Wishart, Rochester, N. Y., assignor, bymesne assignments, to Consolidated Vacuum Corporation, Rochester, N. Y.,a corporation of New York Application March 5, 1952, Serial No. 274,995

4 Claims. (Cl. 230-101) This invention relates to vacuum pumps and isparticularly concerned with high vacuum diffusion pumps.

High vacuum diffusion pumps have come into general use for pumping inthe range below 1' mm. Hg and particularly below about 100 microns Hg.One of the more common types used, particularly with organic pumpfluids, is the vertical fractionating diffusion pump having a boiler, a

generally cylindrical pump casing extending up-' wardly from the boilerwith the open upper end of the casing being flanged for connection to asystem to be evacuated, and one or more vapor chimneys having theirlower end resting on the bottom of the boiler to form a series ofinterconnected boiler compartments and extending upwardly into thecasing to terminate in a jet nozzle assembly. 'For satisfactoryoperation, the bottom of the chimney or chimneys must rest squarely onthe bottom of the boiler, and the chimney should be properly centeredwithin the casing. Since the pumps must be disassembled and cleanedperiodically, ease of disassembly is a desirable feature particularly asregards removal 25 of the chimney and jet assembly.

The conventional vertical diffusion pumps commonly used for many yearsprovided easy removal of the chimneys and jet assemblies since theycould simply be inverted and the chimney and jet assemblies would dropout. Although this arrangement was convenient from the standpoint ofdismantling the pump, the chimney and jet assemblies were readilydamaged by dropping out during shipment, or by someone inadvertentlyturning the pump upside down, or by rapidly admitting air into anevacuated system which blew the chimney and jet assemblies out 'of thepump.

It is accordingly an object of this invention to provide a high vacuumvertical diffusion pump which is readily disassembled but whichovercomes the aforesaid disadvantages of prior art pumps of this type.

Another object of the invention is to provide means "for pinning downthe chimney-jet assemblies without adversely afiec'ting the operation ofthe pump.

Another object of the invention is to provide a vertical diffusion pumpincluding readily insertable and removable means for confining thechimmy and jet assemblies against undesirable vertical displacement.

Another object of the invention is to provide a vertical diffusion pumpincluding means for pin the chimney and jet assembly against verticaldisplacement without interfering with proper seating of the chimneys onthe bottom of the boiler.

Another object of the invention is to provide simple but effective meansfor obviating damage to the jets incase of sudden backsurging of airinto an evacuated system.

Other objects will be apparent from the drawings and. from thedescription and. claims which follow.

These and other objects are attained by apparatus embodying thisinvention as described more fully hereinafter with particular referenceto the accompanying drawings.

Of the drawings:

Fig. 1 is a view in elevation partly broken away and in section of avertical diffusion pump constituting a preferred embodiment of theinvention; and

Fig. 2 is a section taken along line 22 of Fig. 1.

Referring particularly to Fig. 1, a boiler It] for vaporizing pump fluidis formed. by a metal shell ii and a metal bottom plate l2 welded orotherwise secured to shell 'I I. Shell it extends below plate 12 to forma skirt l3 which serves as a base for the pump. The upper end of shell His necked down to a peripheral lip M. A conventional resistance heaterI5 is bolted or otherwise secured to the lower face of plate l2 forheating the boiler, current being supplied by connection to binding postIt and a lead off post (not shown) A generally cylindrical metal pumpcasing it is welded or otherwise secured to the necked down portion ofshell I l, the casing I! being of slightly larger diameter thanperipheral lip I 4 to form an annular gutter It at the top of boiler It. Annular flange l9 welded to the upper end of easing IT is drilled at20, 20 for bolting the pump to a sys tem to be evacuated. An annulargroove 2| in the upper face of flange i 9 serves as a seat for an O-ringgasket to ensure a vacuum-tight seal between the pump and the system tobe evacuated.

A forepressure arm 22 welded or otherwise secured to casing l1 adjacentthe lower end of casing l1 and above boiler l0 provides an outlet portfor the pump. Forepressure arm 22 is provided with a flange 23 forconnecting the outlet port to a backing pump. A coil 24 of copper tubingis wound around casing I1 and forepressure arm 22 and is provided with asuitable connection such as shown at 25 for connecting coil 2'4 to asource of cooling water as well as a similar exit connection (notshown). A separate coil 26 of copper tubing is wound around :shel-l llof boiler 10 and necti-ons 21, 2! for supplying coil 26 with coolingwater. The forepressure arm has a hemispherical dam 28 mounted insidearm 22 for collecting condensed vapors in arm 22. Drain 30 opens out ofarm 22 in front of dam 28, the drain 3!) being closed by screw cap 3|and gasket 32.

Cylindrical vapor chimneys 33, 34 and 35 fabricated of aluminum or othersuitable metal are disposed within casing H in generally concentricrelation with each other and with casing 11. The inner chimney 35 andthe intermediate chimney 34 rest on the bottom l2 of boiler I9 anddivide boiler in into a series of concentric boiler compartments whichare interconnected in series by notches in the lower ends of chimneys 34and 35. The notch in inner chimney 35 is shown at 31, the notch (notshown) in chimney 34 being spaced 180 from notch 31 in order to providea tortuous path through the boiler compartments. Vapor chimneys 33, 34and 35 are connected to each other by rod spacers 38, 38 welded orotherwise secured to the respective chimneys. The lower end of outerchimney 33 extends into gutter l8 formed by lip 14 of shell II and thelower end of easing H. Chimney 33 is secured to intermediate chimney 34by spacers 38, 38 such that the lower end of chimney 33 is out ofcontact with the sides or bottom of gutter I8.

Chimney 33 is provided with a jet cap 44 of aluminum or other suitablemetal welded. to chimney 34 in position to form a jet nozzle assemblywith the upper end of chimney 33. Chimney 34 is likewise provided with ametal jet cap 4! welded to inner chimney 35 to form a jet nozzleassembly with the upper end of chimney 34. The long inner chimney 35which extends to the low pressure region of the casing adjacent theinlet is provided with a metal umbrella cap 42 positioned to form a jetnozzle assembly with the upper end of chimney 35. Umbrella cap 42 ismounted on centering post 43 which in turn is welded or otherwisesecured to the inner wall of chimney 35, thelower end of post 43 beingbent at right angles to the vertical section for contact with thesidewall of the chimney while the centrally'disposed vertical section ofpost 43 projects upwardly above the upper end 'of chimney 35 and its jetcap 42.

The chimney and jet assemblies are pinned against vertical displacementby spring clip 44 desirably consisting of a single length of spring wireextending diametrically across the internal diameter of casing I!immediately above umbrella cap 42. Spring clip 44 is formed with an opencentral loop 46 encircling post 43 and the projecting ends of clip 44extending into close contact with the inner face of casing I! wherebyclip 44 is pinned across the throat of the pump casing. Clip 44 ispreferably dimensioned so that, in its normal looped but untensionedcondition, the clip is slightly longer than the diameter of casing H.The clip 44 is readily inserted by forcing the ends of the clip towardeach other in the direction of the central loop so as to tension theclip, positioning the clip on post 43, and then allowing the clip tospring back towards the untensioned position whereby the ends of thespring wire are pinned firmly against the inner face of the casing withthe springing action of the central loop exerting lateral pressure onthe ends. In the preferred embodiment, the portions of clip 44projecting outwardly from the central loop 46 are slanted slightlyupwardly from the central loop to the ends of the clip whereby pressureupwar ly 4 7 against the center of the clip serves to wedge it moretightly in the casing throat.

The central loop 45 of clip 44' desirably is of slightly larger diameterthan the post 43 which it encircles so that the post has a limited areafor lateral movement. The chimney and jet assemblies are centered in thecasing by spider 4'! welded to chimney 35, the spider 4? beingdimensioned so that it readily fits into casing 41 without jamming.

In the preferred embodiment illustrated in the drawings, the bottomplate 12 of boiler i!) and the heater l5 have a threaded drain 43 tappedtherethrough and opening into the boiler compartment defined by thelower end of inner chimney 35. A hollow, externally threaded plug 58 isscrewed into threaded opening 48, plug 53 being locked in place by locknut 53 and capped by cap and gasket 52. A metal tube 53, having itsupper end projecting through the wall of chimney 35 into the spacebetween chimneys 34 and 35, is secured to and suspended from chimney 3'5with the lower flared end of tube 53 being disposed immediately abovedrain 48.

In fabricating the pump illustrated in the drawings, the boiler H3,heater l5, casing H and forepressure arm 22 are welded or otherwisesecured together into an integral unit. The chimneys 33, 34 and 35,jet-caps 43, 4! and 42 and tube 53 are also assembled as an integralunit. With the drain plug 53 locked in place and capped, the chimney-jetassembly is lowered into casing ll until the lower ends of chimneys 34and 35 are resting squarely on the bottom :2 of boiler l3 and the lowerend of outer chimney 33 hanging in gutter 58. Spider 4'? serves toensure proper centering of the chimneys inside the casing, the spider 47having a loose fit inside casing 47 so that chimneys 34 and 35 can seatsquarely on plate l2 forming the bottom of boiler 10. Proper seating ofchimneys 34 and 35 on plate i2 is important to ensure properfractionating action of the pump fluid without objectionable seepage offluid under the ends of the chimneys 34 and 35.

Spring clip 44 is then tensioned as described hereinabove, slipped onthe post 43, and allowed to spring into pinning position against theinner face of casing H. The diameter of the central loop 46 issuflicient to keep the clip 44 out of contact with post 43 whereby thechimneys can seat freely on the bottom of boiler it.

The assembled pump can then be shipped without elaborate precautions toprotect the chimneyjet assemblies since they are pinned against verticaldisplacement.

In operating the pump embodying the invention, a suitable organic pumpfluid is charged into the boiler, the inlet port flange i3 is bolted tothe system to be evacuated and the forepressure arm is connected to amechanical backing pump by means of flange 23. Cooling fluid iscirculated through coil 24, and the heater is energized to vaporize pumpfluid in the boiler. In

, operation, pump fluid vapors formed in each of the boiler compartmentsascend through the respective chimneys and emerge through the jetnozzles into the casing. The vapors are condensed on the cooled casingwall, the pump fluid condensate runs down into gutter 13 where it formsa liquid seal around the lower end of chimney 33, and the fluidoverflows into the outer boiler compartment between chimney 34 and shellII. The highest vapor pressure components, of the pump fluid arerevaporized in this outer someones i boiler .ieomuanmem and ascend toemerge through the gist nozzle formed by phimneyfit and ilci-gh'yaporzpnessure components the-:remainder er the pump fluid. These con' densedvolatiles usually form only a minor percentage of the pump fluid and canbe dizaum oli through drain plug .39 when operation of the pump isinterrupted.

After the highest vapor pressure components oflthe' pump flu-id aretaps.

in the outer "ng fluid "flows 'ei i-ediate boiler compartment where theintermediate vapor -l-ressure components are evolved and ascend to exerttheir pumping action1 in intermediate p -essure zone of the *purrr-p.remaining low vapor components of the pump fluid flow into the innermostboiler compartment and, after being vaporized, ascend inside chin. my 35and exert their pumping action in the lowest pressure zone of the pumpadjacent the inlet end of the pump.

The tarry residues and decomposition products of the pump fluid tend tocollect in the innermost boiler compartment. Upon prolonged heating,these materials tend to evolve gases which would impair the efiiciencyof the pump permitter to ascend chimney 35. Tube 53 serves to channelsuch gases into a higher pressure zone of the pump, however, where theirdeleterious effect on the pump efficiency is minimized. Drain 48 can beused for draining all or part of the pump fluid from the boiler and tube53 also serves to collect and channel out of the inner compartment anyair which might leak through drain &3.

Occasionally during evacuation operations, vacuum may be broken suddenlydue to failure of some part of the or other cause. When the system isopened suddenly to atmosphere, the back surge of air through the pump issuf ficlent to blow the chimney-jet assembly out of the pump unless theassembly is pinned in place in accordance with this invention. Thespring clip embodying this invention effectively prevents a blowout ofthis kind with its attendant damage to the chimneys and jet caps.

In the pump embodying this invention, how ever, the spring clip isreadily removed when it is to disassemble the pump for cleaning. Theclip does not interfere with the pumping action of the pump since itdoes not block any substantial area of the pump throat, and allows thechimneys to roe-l: slightly so as to seat freely on the bottom of theboiler.

While the invention has been described in considerable detail withreference to a preferred embodiment thereof, it will be understood thatvariations and modifications can be eiiected in the apparatus embodyingthe invention without departing from the spirit and scope of theinvention as described hereinabove and illustrated in the drawings andas defined in the appended claims.

I claim:

pump of the type comprising a generally cy :irical pump casing having anopen upper e adapted to be connected to a system to be evacuated, aboiler opening into the lower end of said pump casing, at

-least ionerriernouable vapor chimney :imvsaid casing generallyconcentric .imeansiandzsaid :nelatima itherewilih, the lower end of saidchimney resiz ng scythe bottom of boiler, the upper .am! of said latig:in an upper none of said cashiglfland jet can cnonerating with saidupper end lorssmcl gag" -noazleas- $&E11Ib1}l, :saddchimney I'beingecured to said boiler and fto' -sniifi casing, the i1 .oueinent whichcomprises means secured to said chimney and phoiectihg rdiy beyondtheupper end of lsatdnhimneyi, and nning means loosely encircling saidpost a and extending outwardly r face of-said casmeans 1 exerting springpressure effective to resist vertical disinto en agement with the roentof said pinning means.

comprising a generally cylindrical pump casing a vertical diffusion"pump of the type having an open upper end adapted to be con- :necteolto asystem to be evacuated, a boiler opening into the lower end of saidpump casing, at least one removable cylindrical vapor chimney disposedin said casing in generally concentric relation therewith, the lower endof said chimney resting on the bottom of said boiler, the upper end ofsaid chimney being in an upper zone of said casing, and jet cap meanscooperating with said chimney and forming therewith a jet'nozzleassembly, said chimney being unsecured to said boiler and to saidcasing, the improvement which comprises post means secured to saidchimney and projecting upwardly beyond the upper end' of said chimney,and pinning means encircling said post means and extending generallydiametrically across the space inside said casing into engagement withthe inner face of said casing, said pinning means comprising a springwire formed with a central loop encircling said post means and the endportions of said wire projecting radially outward from said central loopwith the ends of said wire pressed tightly against said casing, saidcentral loop being of slightly larger diameter than said post means andpermitting limited lateral movement of said post means within said loop.

3. In a vertical diffusion pump of the type comprising a generallycylindrical pump casing having an open upper end adapted to be connectedto a system to be evacuated, a boiler opening into the lower end of saidpump casing, at least one removable cylindrical vapor chimney disposedin said casing in generally concentric relation therewith, the lower endof said chimney resting on the bottom of said boiler, the upper end ofsaid chimney being in an upper zone of said casing, and a jet nozzleassembly including said upper end of said chimney, said chimney beingunsecured to said boiler and to said casing, the improvement whichcomprises a centering post secured to said chimney and projectingupwardly beyond the upper end of said chimney, and pinning meanscomprising a spring wire positioned immediately above the upper end ofsaid chimney and extending across the internal diameter of said casing,said spring wire being formed with a central open loop encircling saidcentering post and end portions extending outwardly from said loop intocontact with the inner face of said casing, said looped spring wirebeing dimensioned to exert positive spring pressure against the innerface of said casing and thereby resist vertical displacement of saidpinning means.

4. In a vertical diffusion pump of the type comprising a generallycylindrical pump casing having an open upper end adapted to be connectedto a system to be evacuated, a boiler opening into the lower end of saidpump casing, at least one removable cylindrical vapor chimney disposedin said casing in generally concentric relation therewith, the lower endof said chimney resting on the bottom of said boiler, the upper end ofsaid chimney being in an upper zone of said casing, and a jet capmounted on said chimney and with said chimney forming a jet nozzleassembly, said chimney being unsecured to said boiler and to saidcasing, the improvement which comprises a centering post secured to saidchimmy and projecting upwardly beyond the upper end of said chimney, andpinning means comprising a single length of spring wire extendinggenerally diametrically across the inner diameter of said casingimmediately above the upper end of said chimney, said spring wire beingformed with a central loop in said wire encircling said J ALIES WISHART.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,435,686 Kuipers Feb. 10, 1948 2,447,636 Colaiaco Apr. 24,1948 2,489,058 Stoltenberg Nov. 22, 1949 FOREIGN PATENTS Number CountryDate 596,964 Great Britain Jan. 14, 1948 an-- h

